Section 18.1. A Summary of the Web Services Platform

18.1. A Summary of the Web Services Platform

The Web services platform (as SOA) is designed to support real-world automated business interactions in which functional and non-functional requirements are much more demanding than in simple Web access to enterprise applications. What are these requirements? In summary, they are:

• The need for interoperable messaging between enterprises and middleware systems with business-level quality of service (secure, reliable, and transactional).

• A framework for describing and discovering services.

• A mechanism for reusing and composing services.

The set of specifications introduced in Chapter 3, "Web Services," and explained in detail in the rest of this book is simply a rendition of these three requirements.

Web services, in spite of their perceived complexity and the number of specifications and standards (or proposed standards), consists at its core of a minimal set of specifications that realize the service-oriented architecture (SOA) computing model. More importantly, the Web services platform and specifications support incremental consumption of capability. It is possible to start with a very small set of capabilities, and then incrementally adopt more of the functions. These are important points to realize. An application scenario can simply start with WSDL to describe services' interfaces, and use SOAP/HTTPS for message interoperability. Increased sophistication in the scenario might require adding partners to the collaboration, motivating the need for WS-Security to implement multiparty authentication, privacy, and integrating these partners using BPEL4WS to coordinate their services. Then, WS-ReliableMessaging can augment the solution to eliminate the need for lost and duplicate message processing from applications. WS-Coordination and WS-BusinessAgreement can complement the BPEL4WS processes to simplify the completion and compensation processing in the business process design. Finally, at each of these incremental stages, WS-Policy and WS-PolicyAttachment provide support for augmenting WSDL with the information necessary to document services expectations and capabilities.

The perceived complexity results from the fact that a much more complex problem is being solved than in prior Web-related standards efforts. Web services supports complex and complete business scenarios, which results in a seemingly complex aggregate set of specifications. Complexity is also due to the proliferation of competing specifications in certain areas. Still, the set of specifications presented in this book is the minimal core set upon which non-trivial business applications can be built in an interoperable, reusable manner. Other proposed specifications extend these ideas into more specific domains, from systems management to resource sharing strategies and industry-specific solutions.